If I search for Firefox in the Android Market on my phone I can't find Firefox! How can I install it on my Phone??
Can you visit this link with your phone?
Also you must note that: Firefox is available for Android phones (2.0 and above) and the Nokia N900.
The official page of Firefox Mobile gives also a list of supported devices that have been tested.
What model/OS/screen size do you have?
Firefox is not supported on all platforms. For example, I can get it on my Nook with Gingerbread, but can't find it on my Froyo Ideos with a tiny screen.